Ampicillin sodium

Ampicillin sodium is a competitive inhibitor of the enzyme transpeptidase with IC50 value of 1.8 μg/ml [1]. 

Ampicillin is a β-lactam antibiotic that kills bacteria by inhibiting transpeptidase reactions. Transpeptidase is involved in the final stages of cell wall biosynthesis and inhibition of it ultimately leads to cell lysis [1]. 

In E. coli 146 cells treated with ether, Ampicillin showed no significant inhibition on the transpeptidase reaction at concentrations below 0.5 μg/ml, but exhibited 50% inhibition at the concentration of 1.8 μg/ml. In E. coli 146 cells, the minimal inhibitory concentration (MIC) of Ampicillin was 3.1 μg/ml [1]. In E. coli and S. typhi, Ampicillin and Epicillin at concentrations close to MIC values killed bacteria at slower rates than Amoxycillin [2]. 

In experimental mouse infections, oral or subcutaneous treatment of Ampicillin at the dose of 0.2 ml/20 g was significantly more effective than Epicillin and Amoxycillin against the majority of infections [2]. 

References:

[1]. Moore B A, Jevons S, Brammer K W. Inhibition of transpeptidase activity in Escherichia coli by thienamycin. Antimicrobial Agents and Chemotherapy, 1979, 15(6): 831-833.

[2]. Basker M J, Gwynn M N, White A R. Comparative activities of ampicillin, epicillin and amoxycillin in vitro and in vivo. Chemotherapy, 1979, 25(3): 170-180.